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[Display omitted] • The specific surface-and phase-sensitive SFG spectroscopy revealed the absolute PS structure at the buried PS/silica interface. • The PS nanolayer near the substrate gradually formed during annealing. • The dewetting occurred at the non-adsorbed PS/the flattened PS nanolayer interface due to the autophobic effect. • As the solvent quality reduced, the dewetting rate of the PS film became slower. • This study provides a molecular-level understanding of the dewetting property of the polymer thin film. Dewetting is a common phenomenon observed from polymer thin films under stimuli, such as annealing, which directly affects the applications of polymer thin films. A key to understanding such dewetting behavior is to precisely probe the molecular structure evolution at the buried polymer/substrate interface during annealing. However, non-destructively probing the buried interface is very difficult at the molecular level and in situ. In this study, the specific surface- and phase-sensitive sum frequency generation (SFG) vibrational spectroscopy was used to investigate PS thin films on silica substrates during annealing. The results showed that the absolute orientation/conformation of PS at the film surface was significantly different from that of the flattened PS nanolayer formed near the substrate by dewetting. The dynamic molecular structure evolution of the PS nanolayer (the formation process of the flattened PS nanolayer) at the buried PS/silica interface was directly observed in situ. The dewetting occurred at the non-adsorbed (bulk, free) PS/the flattened PS nanolayer interface due to the autophobic effect. Furthermore, the effects of end groups and solvents on the PS dewetting rate were also elucidated. This study provides a molecular-level understanding of the PS structure at the buried PS/silica interface and its relationship to dewetting behavior. [ABSTRACT FROM AUTHOR]

In this research, sum frequency generation (SFG) vibrational spectroscopy, a surface and interface specific technique, was used to study chemical interactions occurring at the buried interface between two polymers in situ. More specifically, the chemical reaction at the buried poly (ethylene vinyl alcohol) (EVOH)/maleic anhydride (MAH) grafted polyethylene (MAHgEO) interface was monitored at the molecular level using SFG. This system was compared to a control EVOH/polyethylene (EO) (without MAH) system where no chemical reaction was observed at the interface. Results from the hydroxyl and carbonyl stretching regions contain contributions from the reaction products of EVOH with MAHgEO. SFG results suggest a chemical reaction occurs which increases interlayer adhesion, consistent with adhesion measurements. This work demonstrates that chemical reactions at buried interfaces between two polymers can be probed in situ nondestructively by SFG, and such interfacial reactions are important for the development of designed polymer/polymer interfaces with improved functionality and properties. Image 1 • Maleic anhydride grafted to polyethylene greatly enhanced adhesion at the polyethylene/poly (ethyl vinyl alcohol) interface. • Enhanced adhesion at the interface is due to the interfacial reaction between maleic anhydride and hydroxyl groups of EVOH. • Interfacial reaction was observed non-destructively at the buried polymer interface in situ. [ABSTRACT FROM AUTHOR]